Active magnetic bearings (AMBs) have recently emerged as an attractive technology for controlling the position of a wide range of rotating machinery shafts, particularly for turbomachinery rotors. Reliable and efficient compression systems have been developed and are used in a myriad of industrial process (for example, petroleum refineries, offshore oil production platforms, etc). There is, however, an ever-increasing demand for smaller, lighter, and more compact compression systems.
Compact compressors (also referred to as compact motor-compressors) combine a pressurized, high-speed motor and magnetic bearing system with the compressor in a single, hermetically sealed motor-compressor module. FIG. 1 illustrates a cross-sectional view of a conventional compact compressor 100. The conventional compact compressor 100 has a compressor end 102 and motor end 104. A pressure casing 106 hermetically seals the compressor and the motor. As is illustrated in FIG. 1, active magnetic bearings (AMBs) 108 are used at various locations along the shaft of the compact compressor 100. For example, AMBs may be typically located at the ends of the shaft and, depending on a length of the shaft, at one or more locations between the ends of the shaft.
One drawback is that the AMBs 108 are inside the pressure casing 106 and thus potentially exposed to harmful contaminants in the process stream including liquids, sediments, acids, and/or other aggressive chemical agents. In order to protect the AMBs 108, a housing may be provided around the AMBs 108 to create an isolated environment for the AMBs 108. Such an enclosed bearing is generally known as a “canned” bearing. The housing of a canned bearing also serves to protect the magnetic bearing from damaging external pressures. Conventional cans are often made of a non-magnetic metal. As a result, the magnetic coupling between the stator and the rotor is reduced. Further, using metallic cans may result in eddy current generation in the metallic cans at the interface of the shaft and the stator.
What is needed, then, is a bearing isolation system that isolates the AMBs from the harmful contaminants, maximizes magnetic coupling between the rotor and the stator, and limits deleterious eddy currents generation at the interface of the rotor and the stator.